Get rid of unused class NGPaintFragmentWithContainerOffset

This patch gets rid of unused class |NGPaintFragmentWithContainerOffset| for
improving code health.

Change-Id: I41367bc1801d8adf96858c3fd78d75b4756185be
Reviewed-on: https://chromium-review.googlesource.com/c/1480367
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634504}

third_party/blink/renderer/core/paint/ng/ng_paint_fragment_traversal.h

@@ -13,14 +13,6 @@ namespace blink {
 
 class NGPaintFragment;
 
-// Used for return value of traversing fragment tree.
-struct CORE_EXPORT NGPaintFragmentWithContainerOffset {
-  DISALLOW_NEW();
-  NGPaintFragment* fragment;
-  // Offset relative to container fragment
-  NGPhysicalOffset container_offset;
-};
-
 // Represents an NGPaintFragment by its parent and its index in the parent's
 // |Children()| vector.
 struct CORE_EXPORT NGPaintFragmentTraversalContext {